Plug valves for use in control of the flow of the particulate catalyst in catalytic convertors are shown in U.S. Pat. Nos. 2,668,755 and 2,850,364. The plug valves shown in these disclosures have served quite adequately. A valve of the plug type is typically installed in the bottom of a regenerator vessel. It is mounted adjacent a pipe or conduit which typically extends through the wall of the vessel to position the plug in close proximity to a valve seat, typically located at the end of a pipe or conduit. Catalyst flows through the pipe and is metered past the valve seat by the position of the tapered plug valve. The catalyst is an abrasive material which has a propensity for abrading and wearing away the metal components of the plug valve. This is particularly a problem with the stem below the plug. The stem must work through an opening of specified size in the body of the valve. The vessel itself is pressurized and hence, it is necessary to prevent leakage from the pressurized vessel along the stem where it inserts through the wall of the body of the valve. Moreover, it is desirable to prevent particulate catalyst from working into the spaces between the valve stem and its supporting structure. Particulate catalyst in this area wears the stem away and weakens the structure.
The apparatus of the present invention is an improved plug mounted on a protected stem. The stem is protected in a significant fashion which avoids the problem of stem erosion by the particulate catalyst. The protective plug valve of this particular invention can be used both for the metering valve which admits spent catalyst to the regenerator and the valve which controls the flow of regenerated catalyst from a dense phase fluid bed in a regenerator into a catalytic reaction vessel.
This apparatus is particularly useful in extending the life of a metering valve in a catalyst regenerator. Continued operation of a catalytic reactor, disengager and the catalyst regenerator that is cooperative therewith is essential. When they are brought on line, they are normally intended to operate for months and hopefully for more than one year. During the continued use of such equipment, the valves which control the flow of the particulate catalyst are subjected to the type of wear mentioned above. Wearing of the valve stem of the plug valves which control the flow of the catalyst can become so excessive as to wear through the valve stem and cause it to break. Breakage of the valve stem normally constitutes a catastrophic failure requiring emergency shutdown of the catalytic process and emergency repairs. Shutdown is normally scheduled where maintenance on all parts of the equipment can be completed. An emergency shutdown to repair a single component is extremely undesirable, particularly in view of the fact that the lost revenues may easily exceed several thousand dollars per hour. In view of these circumstances, it will be understood that protection of the valve stem is exceedingly important and this invention provides that type of protection. The present invention protects the valve stem against significant contact with the particulate catalyst. The catalyst may settle in the vicinity of the valve stem but it does not otherwise abrade the surface of the valve stem in significant measure. This invention thus extends the life of the stem substantially and avoids catastrophic shutdowns.